What is the recommended treatment for a patient with chronic Mycobacterium Avium-Intracellulare (MAI) infection as indicated by a computed tomography (CT) chest scan?

Treatment of Chronic Mycobacterium Avium-Intracellulare (MAI) Pulmonary Infection

For chronic MAI pulmonary infection identified on CT chest, initiate combination antimycobacterial therapy with a macrolide (clarithromycin 500 mg orally twice daily OR azithromycin 500 mg daily) plus ethambutol 15 mg/kg orally once daily, with or without rifampin 450-600 mg once daily (or rifabutin 300 mg once daily), and continue treatment for 12 months after sputum culture conversion. 1

Initial Diagnostic Confirmation

Before initiating treatment, confirm the diagnosis meets established criteria:

• Obtain three separate sputum samples or bronchoscopic specimens for acid-fast bacilli culture to establish true infection versus colonization 1, 2
• High-resolution CT (HRCT) chest is the preferred imaging modality and typically shows centrilobular nodules, bronchiectasis (particularly in segments 2,3,4, and 5), and tree-in-bud opacities 1, 3
• Exclude other underlying conditions that predispose to MAI, including cystic fibrosis, immunodeficiency states, HIV infection, primary ciliary dyskinesia, and allergic bronchopulmonary aspergillosis 1

Standard Treatment Regimen

First-Line Therapy (Immunocompetent Patients)

Macrolide-based triple therapy:

• Clarithromycin 500 mg orally twice daily (preferred macrolide) 1

  • Critical warning: Do NOT use clarithromycin 1,000 mg twice daily, as this higher dose is associated with increased mortality 1
  • Alternative: Azithromycin 500 mg orally once daily 1

• Ethambutol 15 mg/kg orally once daily 1

• Rifampin 450-600 mg orally once daily OR rifabutin 300 mg orally once daily 1

  • Rifabutin may be preferred if drug interactions are a concern 4

Treatment Duration

• Continue therapy for a minimum of 12 months after sputum culture conversion 1
• Monitor sputum cultures monthly during treatment to document conversion 2
• For patients with extensive cavitary disease or severe bronchiectasis, consider extending treatment to 18-24 months 5

Special Populations and Considerations

HIV-Positive Patients with Disseminated MAI

• Lifelong suppressive therapy is required after initial treatment of disseminated disease 1
• Use the same macrolide-ethambutol combination with or without rifabutin 1
• Do not discontinue maintenance therapy even if CD4+ counts improve to >100 cells/mm³ with HAART, as insufficient data support stopping 1

Drug Interactions

Critical interactions to monitor: 4

• Rifabutin with clarithromycin: Increases rifabutin levels and decreases clarithromycin levels, with increased risk of uveitis—use with caution and monitor closely 4
• Protease inhibitors: Rifabutin should not be used with certain protease inhibitors; consider rifabutin dose reduction to 150 mg daily or alternative regimens 1, 4
• CYP3A inducers (efavirenz, nevirapine, rifampin) decrease clarithromycin levels while increasing 14-OH-clarithromycin metabolite, potentially reducing efficacy 4

Alternative Regimens

For patients intolerant of first-line therapy: 1

• Add a fluoroquinolone (moxifloxacin or ciprofloxacin 750 mg twice daily) 1, 5
• Consider adding amikacin 15 mg/kg daily IV or IM in divided doses for severe or refractory disease 1
• Avoid clofazimine, as it is associated with adverse clinical outcomes 1

Pregnant Women

• Azithromycin plus ethambutol are the preferred agents during pregnancy 1
• Avoid rifamycins when possible due to potential teratogenicity 1

Monitoring and Follow-Up

• Monthly sputum cultures until conversion, then every 3 months 2
• Chest CT at 6-12 month intervals to assess radiographic response and disease progression 1
• Monitor for drug toxicity: hepatotoxicity (rifamycins), optic neuritis (ethambutol), QT prolongation (macrolides) 1
• Assess for treatment failure if no clinical improvement after 3-6 months or persistent positive cultures after 6 months 1

Surgical Considerations

For localized disease with intolerable symptoms despite maximal medical therapy:

• Surgical resection may be offered for focal bronchiectasis or solitary nodules causing hemoptysis or recurrent infections 1, 2
• Best outcomes occur with complete resection of affected segments 2

Common Pitfalls

• Do not treat colonization: Ensure diagnostic criteria are met before initiating therapy, as MAI isolation alone does not mandate treatment 1, 2
• Do not use monotherapy: Always use combination therapy to prevent resistance 1
• Do not stop therapy prematurely: Treatment must continue for 12 months after culture conversion, not just symptom resolution 1
• Do not ignore drug interactions: Carefully review all concomitant medications, especially antiretrovirals 4